1. Field of the Invention
The present invention relates to a holding structure for holding an object or a workpiece, which is usable in a manipulator, a robot hand, and so forth. More particularly, the present invention relates to a holding structure that is capable of accurately and certainly holding even small objects having a variety of shapes and different sizes.
2. Description of the Related Art
In recent years, downsizing and portability of products are increasingly advanced, and it becomes important to reduce the weight and the three-dimensional profile of the product. Downsizing and variety of components of products are hence increasingly advanced. Further, costs of such products are drastically decreasing, and accordingly the assemblage of components is dominantly performed by using working robots. Especially, as a life cycle of the product becomes short, it becomes important to simplify the working robot and reduce its cost.
Further, micro-machines are greatly anticipated in the future, and there is accordingly a great possibility of necessity for a method of assembling components of new sizes, sorts and profiles. Furthermore, as sizes of components decrease, rigidity and strength of the components are likely to lower. Therefore, a force for holding such components needs to be set to a small optimum magnitude. Morever, taking into a consideration the assemblage efficiency of small components for small products considering interference and the like with surroundings of the components caused when the components are assembled, the size of a holding structure for holding the components also needs to be drastically reduced.
As a hand mechanism for components, there have been conventionally proposed a gripper-type hand, and multi-joint hand mechanism. The gripper-type hand has a feature that its hand structure is simple, while the multi-joint hand mechanism is characterized by a large number of kinematic degrees of freedom for an object to be held. However, in a case of using a robot hand of the gripper type, all workpieces having various and diverse shapes cannot be stably held by a common robot hand. In contrast, in a case of using a robot hand of the multi-joint type, although all workpieces having a variety of shapes can be stably held by a common robot hand, it is difficult to identify a holding point of an object because of a large number of kinematic degrees of freedom present in the robot hand. Further, since the robot hand of this type requires a number of kinematic degrees of freedom, its structure is liable to be complicated. It is hence necessary to control a large number of actuators in a cooperative manner.
In the above-discussed situation, there have been proposed manipulating hands of a gripper type capable of stably holding a variety of objects or workpieces. Japanese Patent Application Laid-Open No. 5(1993)-169387 discloses a hand which includes a finger with a multi-core block comprised of a plurality of independently-movable cores, and in which individual cores can be moved to conform the shape of the finger to the shape of an object such that all of a variety of objects can be stably held. Further, Japanese Patent Application Laid-Open No. 2000-254884 discloses a hand in which a sensor provided in a finger senses a holding force of the finger, and the holding force is controlled by an actuator.
In the above-discussed conventional hands, however, mechanisms and control methods are likely to be complicated, and it is accordingly difficult to reduce the size of a holding structure for holding a small object or workpiece.